REPL: cannot assign variables whose names match a name exported from Base after any tab autocompletion

[yurivish]

If you press tab twice to autocomplete a name, the variable names is no longer assignable in global scope.

In a new REPL session:

julia> f<tab><tab>
factorial   fieldoffset  finalizer    findnext     flipsign     for
false       fieldtype    finally      findprev     float        foreach
falses      filemode     findall      first        floatmax     frexp
fd          filesize     findfirst    firstindex   floatmin     fullname
fdio        fill         findlast     fld          floor        function
fetch       fill!        findmax      fld1         flush        functionloc
fieldcount  filter       findmax!     fldmod       fma
fieldname   filter!      findmin      fldmod1      foldl
fieldnames  finalize     findmin!     flip         foldr
julia> names = 10
ERROR: cannot assign variable Base.names from module Main
Stacktrace:
 [1] top-level scope at none:0

julia> versioninfo()
Julia Version 1.0.2
Commit d789231e99 (2018-11-08 20:11 UTC)
Platform Info:
  OS: macOS (x86_64-apple-darwin14.5.0)
  CPU: Intel(R) Core(TM) i7-3615QM CPU @ 2.30GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-6.0.0 (ORCJIT, ivybridge)
Environment:
  JULIA_EDITOR = subl

I saw a few related issues (e.g. #23677) but am not sure if they describe the same issue. If they do, feel free to close.

[cstjean]

Not just names; any Base function, regardless of what was tab-completed.

julia> sin = 1
ERROR: cannot assign variable Base.sin from module Main
Stacktrace:
 [1] top-level scope at none:0

[mauro3]

Note that in 0.6 this only threw a warning:

julia> sin = 1
WARNING: imported binding for sin overwritten in module Main
1

[JeffBezanson]

Maybe fixed by #29962?

[StefanKarpinski]

No, still happens on master.

[StefanKarpinski]

Weird: I just stopped and restarted Julia and now can't reproduce this. Freshly built Julia. 💢

Here's the entire session, just in case it helps debug this:

               _
   _       _ _(_)_     |  Documentation: https://docs.julialang.org
  (_)     | (_) (_)    |
   _ _   _| |_  __ _   |  Type "?" for help, "]?" for Pkg help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 1.1.0-DEV.790 (2018-12-03)
 _/ |\__'_|_|_|\__'_|  |  Commit a26031e25a (0 days old master)
|__/                   |

julia> ones
ones (generic function with 6 methods)

help?> ones
search: ones leading_ones trailing_ones countlines count_ones to_indices RoundNearest

  ones([T=Float64,] dims...)

  Create an Array, with element type T, of all ones with size specified by dims. See
  also: fill, zeros.

  Examples
  ≡≡≡≡≡≡≡≡≡≡

  julia> ones(1,2)
  1×2 Array{Float64,2}:
   1.0  1.0

  julia> ones(ComplexF64, 2, 3)
  2×3 Array{Complex{Float64},2}:
   1.0+0.0im  1.0+0.0im  1.0+0.0im
   1.0+0.0im  1.0+0.0im  1.0+0.0im

julia> zeros
zeros (generic function with 6 methods)

help?> ones
search: ones leading_ones trailing_ones countlines count_ones to_indices RoundNearest

  ones([T=Float64,] dims...)

  Create an Array, with element type T, of all ones with size specified by dims. See
  also: fill, zeros.

  Examples
  ≡≡≡≡≡≡≡≡≡≡

  julia> ones(1,2)
  1×2 Array{Float64,2}:
   1.0  1.0

  julia> ones(ComplexF64, 2, 3)
  2×3 Array{Complex{Float64},2}:
   1.0+0.0im  1.0+0.0im  1.0+0.0im
   1.0+0.0im  1.0+0.0im  1.0+0.0im

help?> zeros
search: zeros count_zeros set_zero_subnormals get_zero_subnormals leading_zeros

  zeros([T=Float64,] dims...)

  Create an Array, with element type T, of all zeros with size specified by dims. See
  also fill, ones.

  Examples
  ≡≡≡≡≡≡≡≡≡≡

  julia> zeros(1)
  1-element Array{Float64,1}:
   0.0

  julia> zeros(Int8, 2, 3)
  2×3 Array{Int8,2}:
   0  0  0
   0  0  0

julia>
julia> module M
           let x = 1
               f() = x
           end
       end
Main.M

julia> M.f()
ERROR: UndefVarError: f not defined
Stacktrace:
 [1] getproperty(::Module, ::Symbol) at ./sysimg.jl:13
 [2] top-level scope at none:0

julia> module M
           let x = 1
               global f() = x
           end
       end
julia> module M
           let x = 1
               global f() = x
           end
       end
WARNING: replacing module M.
Main.M

julia> M.f()
1

julia> M.x
ERROR: UndefVarError: x not defined

julia> using Dates

julia> 1day
ERROR: MethodError: no method matching *(::Int64, ::typeof(day))
Closest candidates are:
  *(::Any, ::Any, ::Any, ::Any...) at operators.jl:502
  *(::T<:Union{Int128, Int16, Int32, Int64, Int8, UInt128, UInt16, UInt32, UInt64, UInt8}, ::T<:Union{Int128, Int16, Int32, Int64, Int8, UInt128, UInt16, UInt32, UInt64, UInt8}) where T<:Union{Int128, Int16, Int32, Int64, Int8, UInt128, UInt16, UInt32, UInt64, UInt8} at int.jl:54
  *(::Union{Int16, Int32, Int64, Int8}, ::BigInt) at gmp.jl:454
  ...
Stacktrace:
 [1] top-level scope at none:0

julia> 1Day
ERROR: MethodError: no method matching *(::Int64, ::Type{Day})
Closest candidates are:
  *(::Any, ::Any, ::Any, ::Any...) at operators.jl:502
  *(::T<:Union{Int128, Int16, Int32, Int64, Int8, UInt128, UInt16, UInt32, UInt64, UInt8}, ::T<:Union{Int128, Int16, Int32, Int64, Int8, UInt128, UInt16, UInt32, UInt64, UInt8}) where T<:Union{Int128, Int16, Int32, Int64, Int8, UInt128, UInt16, UInt32, UInt64, UInt8} at int.jl:54
  *(::Union{Int16, Int32, Int64, Int8}, ::BigInt) at gmp.jl:454
  ...
Stacktrace:
 [1] top-level scope at none:0

julia> Day(1)
1 day

julia> Date(2014,1,29):Day(1):Date(2014,2,3)
2014-01-29:1 day:2014-02-03

julia> BLAS.gemm!
ERROR: UndefVarError: BLAS not defined

julia> using LinearAlgebra

julia> BLAS
LinearAlgebra.BLAS

julia> BLAS.ge
gemm  gemm!  gemv   gemv!  ger!
julia> BLAS.ge
gemm  gemm!  gemv   gemv!  ger!
julia> BLAS.gemm!
gemm! (generic function with 4 methods)

help?> BLAS.gemm!
  gemm!(tA, tB, alpha, A, B, beta, C)

  Update C as alpha*A*B + beta*C or the other three variants according to tA and tB.
  Return the updated C.

julia>
julia> f

factorial         filesize           findmin!           float
factorize         fill               findnext           floatmax
false             fill!              findprev           floatmin
falses            filter             first              floor
fd                filter!            firstdayofmonth    flush
fdio              finalize           firstdayofquarter  fma
fetch             finalizer          firstdayofweek     foldl
fieldcount        finally            firstdayofyear     foldr
fieldname         findall            firstindex         for
fieldnames        findfirst          fld                foreach
fieldoffset       findlast           fld1               frexp
fieldtype         findmax            fldmod             fullname
fieldtypes        findmax!           fldmod1            function
filemode          findmin            flipsign           functionloc
julia> sin = 1
ERROR: cannot assign variable Base.sin from module Main
Stacktrace:
 [1] top-level scope at none:0

[StefanKarpinski]

This seems to reproduce it reliably in a fresh session:

julia> using Linear<tab>Algebra

julia> sin = 1
ERROR: cannot assign variable Base.sin from module Main
Stacktrace:
 [1] top-level scope at none:0

[StefanKarpinski]

In particular, tab completing names seems to be a red herring—it's neither necessary nor sufficient.

[cstjean]

On a fresh 1.0.2 session, si<tab>n = 1 triggers it every time for me.

[StefanKarpinski]

That's a different (similar) bug and is already fixed on master.